Plasmablastic Myeloma Versus Plasmablastic Lymphoma; Is MYC Rearrangement Helpful Towards A Precise Diagnosis?

Abstract

Abstract Introduction/Objective Plasmablastic myeloma (PBM) is a rare and aggressive plasma cell neoplasm. Differentiating PBM from plasmablastic lymphoma (PBL) represents a diagnostic challenge, as both diseases have overlapping cytomorphologic and immunophenotypic features. Genetic mutations in MYC occur in a majority of PBL cases but rarely in PBM, thus can theoretically be used to differentiate between both neoplasms. Methods We report a case of a 53-year-old female who presented with a rapidly growing mass in her right mandible. Biopsy revealed circumscribed nodules of immunoblastic cells with moderate cytoplasm, large vesicular nuclei and large prominent nucleoli. Apoptotic debris and brisk mitoses were present. Molecular testing revealed a C-MYC rearrangement. The location of the neoplasm and the above described morphological features were suggestive of PBL, especially with a positive C-MYC rearrangement. The neoplastic cells were positive for CD138, MUM1,CD56 and kappa; and negative for CD45, CD20, PAX5, CD3, CD5, CD30, EBER-ISH, HHV8, ALK-1, Lambda, EMA, CD21, CD23, pancytokeratin, CK20, CK7, Cam5.2, chromogranin, synaptophysin, HMB45, S100, P16, P40. MIB-1 showed high positivity, approximately 95%. Results Patient underwent further diagnostic work up, her HIV antibodies result were negative however, she was found to be anemic (Hemoglobin 6.6 g/dl; reference range 12-16 g/dl) and hypercalcemic (Calcium 12.3 mg/dl; reference range 8.5-10.5 mg/dl). PET scan revealed multiple hypermetabolic lytic bone lesions. The bone marrow biopsy showed 80% cellularity with extensive involvement by atypical plasmacytic cells forming large clusters. The patient’s final diagnosis was PBM. Conclusion Differentiating PBM from PBL is essential as treatment is different. Although MYC rearrangement in PBM is not common, it has been demonstrated and therefore should not be used to exclude this diagnosis. Here, we highlight the importance of correlating detailed clinical, radiological, laboratory, histological and genetics data for reaching the final diagnosis.